Orthodontic brackets attach directly to teeth and serve to transmit corrective forces from an orthodontic archwire to the tooth to which the bracket is attached. The requirements for an orthodontic bracket are quite severe. First, it must have sufficient mechanical strength to withstand the forces to which it will be subjected, including the forces transmitted by an archwire, ligation forces, and mastication forces. Second, it must be chemically inert in the oral environment so that it will not corrode and will be and remain biologically inert. The bracket must meet these requirements, and still remain small enough to fit on the tooth. Despite proposals for making orthodontic brackets from many different materials, the overwhelming majority of orthodontic brackets in use today are made of metal, usually stainless steel. Metal brackets meet all of the essential requirements, but they have one undesirable attribute--they are unsightly. A person undergoing orthodontic treatment has a conspicuous amount of metal in full view on the front surfaces of his or her teeth. And since the treatment may extend over a number of years, this unsightly appearance must be endured for a considerable period of time.
The incentive to make brackets from less unsightly materials has existed for many years. But recently, orthodontic treatment has been given to increasing numbers of adults, for whom the unsightly appearance of metal brackets is more than a mere annoyance. Therefore, the incentive to provide more esthetic orthodontic treatment is even greater now than it has ever been.
To avoid the unsightly appearance of metal orthodontic brackets, it is possible in some (but not all) cases to install the brackets and archwire on the lingual (tongue) side of the teeth. However, the lingual side technique usually takes longer and is usually more expensive than the customary buccal side technique to complete the treatment. Also, the brackets and archwire sometimes interfere with the tongue during speech. It has been proposed to make orthodontic brackets out of less unsightly material, such as transparent or translucent plastic (e.g., polycarbonate), or ceramic materials which more closely resemble natural dentition. A problem with both plastic materials and ceramics is that their mechanical strengths are border-line, and bracket breakage or creep can be a significant problem with them. The ceramic brackets that are currently in use are rather bulky (to overcome the physical property limitations of the material), so they tend to be somewhat uncomfortable to the patient. From an esthetic viewpoint, neither plastic nor ceramic materials are fully satisfactory either, because plastic may discolor (from coffee, tea, tobacco, and various foods), and the color of ceramic rarely exactly matches natural dentition. In an effort to overcome the strength limitations of ceramic and plastic brackets, it has been proposed to reinforce such plastic brackets with metal inserts or metal liners (for the archwire grooves). While this may help (although it will not completely alleviate) the strength limitations of plastic or ceramic brackets, such solutions bring back, to a least a limited degree, the esthetic problem for which the plastic or ceramic bracket was the proposed solution. Thus, to date, there are no commercially available orthodontic brackets that satisfactorily solve the above-described esthetic problem.
It has been proposed by the inventors herein to make orthodontic brackets from single crystal alumina (sapphire). For instance, see U.S. patent application Ser. No. 743,851, filed June 12, 1985, now U.S. Pat. No. 4,639,218. Such sapphire brackets are an excellent solution to the esthetic problem, but they are rather expensive and are not yet commercially available.